Somali pirates are building up their defences around a captured Saudi Arabian super-tanker after demanding a $25 million ransom for the ship and its huge cargo of crude oil.

As foreign warships steam into the area and shipping companies work out alternative routes for their vessels, extra militiamen and other fighters are being brought into the pirate lair of Harardhere.

“Some of them are inside the town and others are taking shelter in a nearby village and can be called if need be,” Mohamed Awale, a local resident, told AFP. He said the fighters had come from the neighbouring Gulgudud and Mudug regions.

They were not the only arrivals in the town. Islamist militiamen and hardline Shebab fighters were also pouring into the town, although it was unclear whether they were angered by the capture of a Saudi boat or simply wanted their share of the loot.

“There are many militiamen who have arrived in the town and they want to get a share from the pirates if the ransom is paid,” said Ahmed Abdullahi, a local elder. “They believe this ship is huge and the owner will pay a lot of money."

The Sirius Star, the biggest ship ever hijacked was seized last Saturday and taken to Harardhere, 180 miles north of Mogadishu. It is fully laden with 2 million barrels of oil, worth around $100 million. Among its 25 crew are two Britons, the chief engineer and the first officer.

The pirates yesterday gave the ship's owners 10 days to pay a $25 million ransom. Speaking from the tanker, a pirate who identified himself as Mohamed Said threatened “disastrous” consequences should Vela International, shipping arm of the Saudi oil giant Saudi Aramco, fail to comply.

“The Saudis have 10 days to comply, otherwise we will take action that could be disastrous,” he said.

Mr Said did not specify the threatened action but the 330m (1,000-ft) tanker is carrying more than 80 million gallons of crude and environmentalists have warned of a huge catastrophe if its tanks are breached.

A Ukrainian ships seized by the same group of pirates in September with a cargo of tanks and other weaponry, the MVFaina, is believed to have been booby trapped to prevent a rescue attempt.

With close to 100 attacks on ships in the Gulf of Aden and Indian Ocean this year, the pirates now pose a growing threat to international trade.

Pirates with no confirmed links to bigger organisations and relatively modest means have seized ships of all sizes and in an ever larger area. The Saudi super-tanker is believed to have seized in just 16 minutes by two speedboats full of pirates armed with Kalashnikov assault rifles and rocket-launchers.

The United States said it would seek support at the United Nations for a resolution to tighten international measures against Somali pirates. Meanwhile, the Saudi Foreign Minister Prince Saud al-Faisal said he was opposed to any negotiations with pirates although he has confirmed that the owners of the Sirius Star are talking with the bandits.

“Like terrorism, it is an evil that has to be eradicated,” Prince Saud told reporters in Oslo.

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